Note 8 - Loans - Allowance for Loan Losses by Portfolio Segment and Based on Impairment Method (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Loans individually evaluated for impairment, allowance	$ 3,833		$ 3,833		$ 2,134
Loans individually evaluated for impairment, balance	137,214		137,214		117,353
Loans collectively evaluated for impairment, allowance	118,066		118,066		121,145
Loans collectively evaluated for impairment, balance	13,211,523		13,211,523		12,752,937
Loans, allowance	121,899		121,899		123,279
Loans	13,348,737		13,348,737		12,870,290
Beginning Balance	122,084	$ 115,544	123,279	$ 118,966
Provision/(credit) for possible credit losses			(3,000)	(2,500)
Charge-offs	(878)	(527)	(897)	(2,285)
Recoveries	693	792	2,517	1,628
Net (charge-offs)/recoveries	(185)	265	1,620	(657)
Ending Balance	121,899	115,809	121,899	115,809
Reserve for impaired loans	3,833	1,561	3,833	1,561
Reserve for non-impaired loans	118,066	114,248	118,066	114,248
Reserve for off-balance sheet credit commitments	3,088	4,513	3,088	4,513
Commercial Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	2,463		2,463		43
Loans individually evaluated for impairment, balance	52,739		52,739		43,495
Loans collectively evaluated for impairment, allowance	52,716		52,716		49,753
Loans collectively evaluated for impairment, balance	2,523,910		2,523,910		2,417,771
Loans, allowance	55,179		55,179		49,796
Loans	2,576,649		2,576,649		2,461,266
Beginning Balance	54,597	47,276	49,796	49,203
Provision/(credit) for possible credit losses	920	(340)	4,827	(1,556)
Charge-offs	(488)	(527)	(507)	(1,730)
Recoveries	150	335	1,063	826
Net (charge-offs)/recoveries	(338)	(192)	556	(904)
Ending Balance	55,179	46,744	55,179	46,744
Reserve for impaired loans	2,463	144	2,463	144
Reserve for non-impaired loans	52,716	46,599	52,716	46,599
Reserve for off-balance sheet credit commitments	1,606	2,583	1,606	2,583
Real Estate Construction Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance
Loans individually evaluated for impairment, balance	8,040		8,040		8,185
Loans collectively evaluated for impairment, allowance	20,663		20,663		24,838
Loans collectively evaluated for impairment, balance	573,877		573,877		670,620
Loans, allowance	20,663		20,663		24,838
Loans	581,917		581,917		678,805
Beginning Balance	21,864	19,768	24,838	23,268
Provision/(credit) for possible credit losses	(1,245)	(1,971)	(4,263)	(5,520)
Charge-offs
Recoveries	44	47	88	96
Net (charge-offs)/recoveries	44	47	88	96
Ending Balance	20,663	17,844	20,663	17,844
Reserve for impaired loans
Reserve for non-impaired loans	20,663	17,844	20,663	17,844
Reserve for off-balance sheet credit commitments	1,207	1,707	1,207	1,707
Commercial Real Estate Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	1,036		1,036		1,738
Loans individually evaluated for impairment, balance	61,953		61,953		52,664
Loans collectively evaluated for impairment, allowance	32,940		32,940		35,872
Loans collectively evaluated for impairment, balance	6,553,838		6,553,838		6,430,031
Loans, allowance	33,976		33,976		37,610
Loans	6,615,791		6,615,791		6,482,695
Beginning Balance	34,230	35,960	37,610	34,864
Provision/(credit) for possible credit losses	(533)	477	(4,696)	1,840
Charge-offs	(161)		(161)	(555)
Recoveries	440	403	1,223	691
Net (charge-offs)/recoveries	279	403	1,062	136
Ending Balance	33,976	36,840	33,976	36,840
Reserve for impaired loans	1,036	1,019	1,036	1,019
Reserve for non-impaired loans	32,940	35,821	32,940	35,821
Reserve for off-balance sheet credit commitments	77	74	77	74
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	334		334		353
Loans individually evaluated for impairment, balance	14,482		14,482		13,009
Loans collectively evaluated for impairment, allowance	11,728		11,728		10,660
Loans collectively evaluated for impairment, balance	3,555,838		3,555,838		3,229,345
Loans, allowance	12,062		12,062		11,013
Loans	3,570,320		3,570,320		3,242,354
Beginning Balance	11,372	12,526	11,013	11,620
Provision/(credit) for possible credit losses	860	1,831	1,135	2,729
Charge-offs	(229)		(229)
Recoveries	59	7	143	15
Net (charge-offs)/recoveries	(170)	7	(86)	15
Ending Balance	12,062	14,364	12,062	14,364
Reserve for impaired loans	334	398	334	398
Reserve for non-impaired loans	11,728	13,966	11,728	13,966
Reserve for off-balance sheet credit commitments	190	143	190	143
Consumer Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance
Loans individually evaluated for impairment, balance
Loans collectively evaluated for impairment, allowance	19		19		22
Loans collectively evaluated for impairment, balance	4,060		4,060		5,170
Loans, allowance	19		19		22
Loans	4,060		4,060		5,170
Installment and Other Loans [Member ]
Loans	4,060		4,060		$ 5,170
Beginning Balance	21	14	22	11
Provision/(credit) for possible credit losses	(2)	3	(3)	7
Charge-offs
Recoveries
Net (charge-offs)/recoveries
Ending Balance	19	17	19	17
Reserve for impaired loans
Reserve for non-impaired loans	19	18	19	18
Reserve for off-balance sheet credit commitments	$ 8	$ 6	$ 8	$ 6